1. Field of the Invention
The present invention relates to a video signal processor for detecting motion by using a composite video signal, more particularly relates to a video signal processor for detecting motion by analyzing a video signal obtained by a so-called three-dimensionally Y/C separated (luminance signal and color signal separated) video signal and improving the precision of motion detection and a TV receiver using the same.
2. Description of the Related Art
A composite video signal, that is, a composite color video signal, includes a luminance signal, a carrier color signal, and a synchronization signal. A TV receiver separates the luminance signal (Y signal) and the carrier color signal (C signal) from the received composite video signal (hereinafter, referred to as “Y/C separation”) to reproduce the color video signal.
Advances in semiconductor integrated circuits have resulted in TV receivers being given built-in line memories for storing video signals in line units and frame memories for storing video signals in frame units. For this reason, the method of performing Y/C separation by comb filters utilizing correlation of luminance signals and carrier color signals between adjacent lines and frames is generally employed.
In the NTSC system of composite video signals, the phases of carrier color signals of composite video signals of adjacent horizontal scan periods are inverse. By utilizing this property, Y/C separation can be realized by a logical operation between video data of the adjacent horizontal scan periods. With this method, however, if there is no correlation between the video signals of adjacent horizontal scan periods, error arises in the result of the Y/C separation, carrier color signal components remain in the separated Y signals, and so-called dot interference occurs, so there is a possibility of deterioration of the image quality. Further, there is also a possibility of the level of the separated carrier color signals being lowered and the reproduced signals ending up deteriorating.
To deal with this problem, the method of monitoring vertical correlation among three adjacent lines and detecting characteristics of pictures of the video signals has been proposed. Among lines having vertical correlation, Y/C separation is carried out by band pass filters in the vertical direction, that is, line comb filters, to reproduce the luminance signals and the color signals. On the other hand, when there is no vertical correlation between the adjacent lines, so-called adaptive two-dimensional comb filters for performing Y/C separation using band pass filters in the horizontal direction in place of the line comb filters to reproduce the luminance signals and the color signals has been proposed. As another method of Y/C separation, use can be also made of so-called motion adaptive three-dimensional comb filters for performing Y/C separation for portions judged to have motion in a field of a video signal by two-dimensional comb filters, extracting a difference signal of the composite video signals in one frame, that is, a C signal, by the frame comb filters for a still portion, and further subtracting the C signal from the composite video signals to thereby generate the Y signals. In the motion adaptive three-dimensional comb filters, it is necessary to correctly detect motion from the composite video signals.
FIG. 12 is a circuit diagram of an example of a video signal processor for detecting motion by using composite video signals of three adjacent lines between two continuous frames. As illustrated, this video signal processor detects motion of the luminance signals (Y motion) and motion of the carrier color signals (C motion) based on video signals CVHc0, CVHc1, and CVHc2 of three adjacent lines in the composite video signals of one current frame and video signals CVHp0, CVHp1, and CVHp2 of three adjacent lines in one past frame and outputs a motion coefficient MVC based on the results of the detection.
As shown in FIG. 12, this video signal processor has comb filters 10 and 20, a Y motion detection circuit 30, and a C motion detection circuit 40. Below, an explanation will be given of these components.
The comb filter 10 receives the video signals CVHc0, CVHc1, and CVHc2 of three adjacent lines in the current frame, performs Y/C separation, and outputs a Y signal Ycur and a color signal Ccur of three lines' worth of video signals in the current frame.
The comb filter 20 receives the video signals CVHp0, CVHp1, and CVHp2 of three adjacent lines in one past frame, performs Y/C separation, and outputs a Y signal Ypst and a color signal Cpst of these three lines' worth of video signals in the past frame.
The Y motion detection circuit 30 calculates a difference between the Y signals Ycur and Ypst generated by the three-line comb filters 10 and 20 of the current frame and the past frame and outputs the amount of the difference as the amount of motion. Further, the level of a high frequency component (color component) generated by the three-line comb filter is judged by a C level judgment circuit 32. When the result of the judgment is that the level of the C component is large, the amount of difference of the Y signal is output through a low pass filter 33 to a Y motion coefficient generation circuit 34, while when it is that the level of the C component is small, the amount of difference of the Y signal is output as it is to the Y motion coefficient generation circuit 34. This is because, in a picture where there is no correlation of sub carriers in the vertical direction (color sub-carrier waves), for example, color horizontal lines or oblique lines, due to the phase relationship of the chroma (color signals), the sub-carrier components remain in the Y signals of the outputs of the three-line comb filters, and a difference of the Y signals is generated also in a still image. If the difference is judged as an amount of motion as it is, a portion of a still image will be erroneously decided as a moving picture portion. In order to suppress the influence of the sub-carriers, the Y motion detection circuit 30 limits the band of the difference of the Y signals by the low pass filter 33. The Y motion coefficient generation circuit 34 receives the judgment result of a vertical edge judgment circuit 35, converts it to its absolute value, performs coring, eliminates isolated dots, adjusts the gain, and outputs a Y motion coefficient MVCy.
In the C motion detection circuit 40, a chroma correlation detector 41 detects the horizontal correlation of the sub-carriers of chroma or the correlation between lines. An amount of motion is generated in an oblique line in the same way as Y motion detection. Therefore, when both of horizontal correlation of the sub-carriers of chroma and correlation between lines are detected, these differences are calculated using the color signals Ccur and Cpst of the current frame and the past frame output by the comb filters 10 and 20. On the other hand, when there is no correlation, the color signals Ccur and Cpst are replaced by 0. Then, a difference calculation circuit 42 calculates the difference of the color signals Ccur and Cpst. The output of the difference calculation circuit 42 is converted to an absolute value, subjected to coring, and adjusted in gain in the C motion coefficient generation circuit 43. The result is output as a C motion coefficient MVCc.
In this way, in the C motion detection circuit 40, by taking the difference of the color signals separated from the composite video signals between frames, in the case of a moving picture having motion, the noncorrelated portion shifts and can be extracted as the amount of motion.
This related art is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 9-46726 and Japanese Unexamined Patent Publication (Kokai) No. 10-191385.
Summarizing the problems to be solved by the invention, in the above video signal processor of the related art, in the high frequency band of colored luminance signals, the sensitivity of the Y motion detection becomes low. As a result, an afterimage of the Y high frequency band appears. Since the C motion detection takes the difference of the absolute values of the sub-carriers, in a portion where the phase of the color is shifted by 180°, the amount of motion of the color is detected as 0 and it is erroneously judged as a still portion without motion. As a result, there is the disadvantage that the motion of only color having no luminance difference cannot be detected, the afterimage of the color or the sub-carrier of chroma leaks into the Y signals by the three-dimensional Y/C separation due to the erroneous judgment of the motion detection, and so-called dot interference of the display of a dot image occurs.
In the above conventional motion detection, provisional Y/C separation is carried out by the output of the three-line comb filter. The difference among these frames is defined as the amount of motion, so it is easily judged that a still image of a horizontal line or oblique line in which the correlation of chroma is lost among lines has motion. In order to avoid this, when it is judged that there is color, this is passed through the low pass filter. As a result, however, the sensitivity of the motion detection is lowered in the high frequency band of the Y signals. Conversely, when trying to detect up to the high frequency band of the Y signals, it is judged that there is motion in the high frequency band of an oblique line, so there is a problem that the portion of a still image flickers.
Further, as explained above, by taking the difference of absolute values of the sub-carriers by the C motion detection, motion of color having a phase of the carrier color signal shifted by 180° is no longer detected. As a result, it becomes impossible to detect motion of only color having no luminance difference, and dot interference occurs due to the erroneous judgment of the motion detection.
Furthermore, in the conventional motion detection, since the calculation of the amount of motion is replaced by 0 according to the presence of the correlation of chroma, in the C motion detection of a still image of an image pattern in which the Y signal has correlation like chroma at an oblique line near the colored sub-carrier frequency fsc, one frame has correlation, and the other frame does not have correlation, so erroneous judgment that the still image has motion is carried out. As a result, an oblique line of the still image is separated by the line comb filter, and deterioration of the band of the Y signal occurs.